1. Field of the Invention
The present invention relates to a privacy communication method and a privacy communication apparatus employing the same. More specifically, the present invention relates to a privacy communication method and a privacy communication apparatus employing the same adapted for communication in a wire manner or a wireless manner upon processing of a signal for maintenance of privacy.
2. Description of the Prior Art
A problem arises in wire communication or wireless communication that a transmitted signal can be received by anyone by the use of a receiving apparatus suited for that purpose. Therefore, a so-called a privacy communication system has been put into practical use in which a transmitted signal is processed in a specific manner so that the signal may not be understood by a person having a general purpose receiver, even if received, while the transmitted signal is received by a specified receiver having a reproducing means for reproducing the above described processed signal.
As such a privacy communication system, a frequency inversion system, a frequency splitting and inversion system, and the like have been conventionally well-known and widely used.
Figs. 1A and 1B are views for explaining a frequency inversion system taken by way of an example of a conventional privacy communication system and FIGS. 2A and 2B are views for explaining a frequency splitting and inversion system taken by way of another example of a conventional wireless privacy communication system.
Referring to Figs. 1A and 1B, the frequency inversion system is adapted such that a carrier wave is modulated with a voice signal to be transmitted and a voice frequency spectrum is inverted by adopting a difference component between the carrier wave frequency and the voice signal frequency, whereupon the same is transmitted, while the reversed processing is applied on the part of a receiver to restore a received signal of a normal voice frequency spectrum. For example, a carrier wave of 3,250 Hz is modulated by a voice signal with a normal voice frequency spectrum of 250 to 3,000 Hz, as shown in FIG. 1A, whereupon a difference between the carrier wave frequency and the voice signal frequency is evaluated to provide a voice frequency spectrum, as frequency inverted, such that 250 Hz is inverted to 3,000 Hz and 3,000 Hz is inverted to 250 Hz. On the other hand, on the side of a receiver, conversely a carrier wave of 3,250 Hz is modulated by the received signal with the voice frequency spectrum as frequency inverted such that 250 Hz is converted to 3,000 Hz and 3,000 Hz is inverted to 250 Hz, as shown in FIG. 1B, whereby a proper voice frequency spectrum of 250 to 3,000 Hz is restored. However, of late, most of communications have been changed from a double-side band communication system to a single-side band communication system and a privacy communication system of frequency inversion has been becoming more valueless.
By contrast, a frequency splitting and inversion system is adapted such that, as shown in FIGS. 2A and 2B, a communication band is split into a plurality of sub-bands by means of a plurality of band filters, whereupon frequency inversion is independently made in each of the bands or rearrangement of the frequency positions is made among the sub-bands, whereupon the signal is transmitted. Referring to the FIG. 2A, the communication band of 250 to 3,000 Hz is equally divided into five sub-bands A, B, C, D and E by means of band filters of a band width of approximately 550 Hz, whereupon the sub-bands A and C is frequency inverted while the sub-bands B, D and E are rearranged. In such a case, possible different combinations of the sub-bands could be 2.sup.5 .times..sub.5 P.sub.5 =32.times.5!=3,840. The above described system is used in wireless communication using a short wave as the A4 privacy communication system; however, disadvantages are involved that the circuit construction becomes extremely complicated and the system becomes large scaled.